This is a highly modified version of a post that appeared back at my old blog quite some time ago. Since it involves a quiz of sorts, I'm not going to post the link back to the original right now. The post with the "answers" will appear on Monday, also slightly modified from the original.
Taxonomy and systematics are the areas of biology that are involved in describing groups of organisms and determining how they relate to one another. One of the jobs associated with these disciplines involves trying to figure out whether or not two different populations of organisms should be considered to be part of the same species. Sometimes this is an easy job - it's pretty clear, for example, that polar bears and penguins are very different sorts of thing. Other times, it's a very hard job. The example I'm going to give you in this post is a difficult case, but a real one. I'll give you the details, and you can take your best stab at the question. On Monday, I'll tell you what the "official" view is.
There are three populations of a flying insect. These populations are physically separated from each other by areas of inhospitable terrain, and members of the populations are not known to come into contact with each other in the wild. Population A is found about 15 km to the northwest of Population B; Population B is found about 50 km to the northwest of Population C. In the past, the areas occupied by Populations A and B were closer together, and may actually have formed a single area. The area where Population C lives was never in contact with the other two populations.
There are no apparent differences between Population A and Population B in either physical appearance or in a specific reproductive behavior. Population C has legs that are a different color from the legs in the other two populations, but is otherwise identical in appearance. The reproductive behavior seen in Population C is very different from that seen in Populations A and B.
The organisms were captured and bred in the laboratory. Experimental crosses were made for the different combinations of these three populations, with the following results:
Table 1: Fertility of male hybrid offspring. The origin of the father is shown in red; the origin of the mother in blue. Fertility was measured as the percentage of male offspring with motile sperm.
Table 2: Viability of female hybrid offspring. "Normal" indicates that the cross produced roughly equal numbers of male and female offspring. "Reduced" indicates that the cross produced a very small number of viable females. Origin of father in red; origin of mother in blue.
My question for you is this: How many different species should these three populations be grouped in, and why? I'll post both the "official" answer and some more information about these animals on Monday.